“What ISO are you at?”

It’s one of the most common questions among photographers in the field, and for good reason. Pick the right ISO for the situation and you have a broader range of shutter speeds and apertures to play with to nail the perfect shot. But muck it up and you may find yourself looking at grainy, noisy, unusable pictures when you get back to your computer, or worse yet, blurry photos that get machine-gunned down under your “Delete” key.

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So how do you figure out the right ISO for the lighting conditions at hand, and how do you determine what each camera in your bag is capable of in terms of ISO performance?

When I get a new camera, one of the first things I do is test it out at various ISO settings to see what my desired ISO limits and upper ISO limits are for decent lighting conditions (e.g. midday on a cloudy day) and for low light conditions, such as before sunrise on a sunny day or after sunrise on a cloudy day. For my so-called desired limits, I want to find out what the maximum ISO is that I’m comfortable using in low light and decent light that will result in a final file that can be used for anything from a 20” x 30” print to a double-page spread in a coffee table book. On the other hand, for my upper limits, I’m looking to discover …